This invention relates to a flat-panel display device. More particularly, the invention relates to a cold cathode fluorescent lamp (CCFL) backlight device used in conjunction with a liquid crystal display (LCD).
Liquid crystal displays (LCD's) used in televisions, computers and other video display devices produce predetermined images and control light transmission to produce video displays. LCD's are particularly suited for flat panel displays because of their superiority in resolution, color image display, and image quality. LCD's do not emit light themselves and therefore utilize backlight devices behind the LCD panel to produce a visible video display. Cold cathode fluorescent lamps (CCFL's) have been used for various illumination purposes and are particularly suited for use as backlight apparatuses for liquid crystal displays, such as TFT-LCD's (Thin Film Transistor-Liquid Crystal Displays) in televisions, computers, and other video display technologies. The performance and quality of the video display is optimized when the illumination is sufficient and uniform throughout the display. Non-uniform illumination degrades the quality of the displayed image. Technological advances in the video display industry enable the production of increasingly larger LCD's and other video displays, and as such video display devices become larger, it becomes increasingly more challenging and important to provide a uniformly illuminated display device. In particular, as larger video displays are produced, it becomes more challenging and important to provide a CCFL backlight apparatus that produces uniform illumination.
Conventional CCFL's that are disposed behind LCD panels typically have one terminal coupled to and driven (i.e. illuminated) by a transformer and an opposed terminal coupled to ground. FIG. 1 shows a conventional CCFL driving device according to the prior art. FIG. 1 shows CCFL 1 having a first terminal 9 coupled to transformer 7 and opposed terminal 11 coupled to ground 13. Transformer 7 drives CCFL 1 by providing a high voltage signal to terminal 9. CCFL 1 has length 3 and as length 3 increases along with the demands of advancing technology to provide larger video displays, a voltage drop occurs across the length 3 of CCFL 1. More particularly, as length 3 increases, a thermometer effect causes the high voltage applied at terminal 9 to be dissipated and a lower voltage to result in the portion of CCFL 1 closest to end 15 and by grounded opposed terminal 11. This results in uneven lighting. In fact, a shortcoming of a CCFL driven using the conventional arrangement shown in FIG. 1, is that the voltage drop may result in the effectuation of an inadequately illuminated dark region 5. In particular, it has been found that, when length 3 is about 30 inches or longer, a dark region such as dark region 5 routinely results.
It would be therefore desirable to produce a CCFL that provides uniform illumination, even as the size of the CCFL increases.